This project addresses the development and evaluation of a prototype laser Raman scattering gas sensor. Potential application areas are: blood pO2/pCO2 via suitable sampling catheter and noninvasive monitoring of respiration, anesthesia delivery, lung function and cardiac output. Mass spec, while currently the most popular approach to medical gas quantitation, suffers from inherent user unfriendliness, high cost and bulkiness. Raman gas scattering should be more attractive from the standpoint of low cost, simplicity and versatility. The prototype incorporates three innovations which make such an instrument possible: (1) Use of laser intracavity gas sampling to increase effective optical power by a minimum of 100 - thus making the use of lower power, cheaper commercial lasers possible; (2) use of six-cavity, high out of band rejection (greater than one million), dielectric filters as substitutes for an expensive, bulky Raman spectrometer; and (3) use of relatively inexpensive silicone avalanche photodiodes as an alternative to a cooled photomultiplier tube and photon counting. Prototype evaluation will consider: sensitivity and specificity for relevant gases, an evaluation of several detector types, long-term system performance trials and preliminary manufacturing cost estimates. Raman spectra and relative scattering cross sections will be determined for five anesthesia gases.